Cost and Related Accumulated Amortization of Flying assets, Facilities and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013	Apr. 30, 2012	Apr. 30, 2011
Property, Plant and Equipment [Line Items]
Cost		$ 1,240,467	$ 1,318,964
Accumulated depreciation		(213,607)	(185,465)
Net book value	1,186,376	1,026,860	1,133,499
Flying Asset
Property, Plant and Equipment [Line Items]
Cost		1,029,381	1,117,338
Accumulated depreciation		(156,345)	(142,024)
Net book value		873,036	975,314
Equipment
Property, Plant and Equipment [Line Items]
Cost		81,802	65,657
Accumulated depreciation		(24,992)	(13,622)
Net book value		56,810	52,035
Facilities
Property, Plant and Equipment [Line Items]
Cost		129,284	135,969
Accumulated depreciation		(32,270)	(29,819)
Net book value		$ 97,014	$ 106,150

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

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Gross amount of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

Amount, net of accumulated depreciation, depletion and amortization, of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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